Alternative splicing determines the post-endocytic sorting fate of G-protein-coupled receptors.
Mu-type opioid receptors are physiologically important G-protein-coupled receptors that are generally thought to recycle after agonist-induced endocytosis. Here we show that several alternatively spliced receptor variants fail to do so efficiently because of splice-mediated removal of an endocytic sorting sequence that is present specifically in the MOR1 variant. All of the recycling-impaired receptor variants were found to undergo proteolytic down-regulation more rapidly than MOR1, irrespective of moderate differences in endocytic rate, indicating that alternative splicing plays a specific role in distinguishing the trafficking itinerary of receptors after endocytosis. The recycling-impaired MOR1B variant was similar to MOR1 in its ability to mediate opioid-dependent inhibition of adenylyl cyclase, and to undergo opioid-induced desensitization in intact cells. Functional recovery (resensitization) of MOR1B-mediated cellular responsiveness after opioid removal, however, was significantly impaired (4-fold reduction in rate) compared with MOR1. To our knowledge the present results are the first to establish a role of alternative RNA processing in specifying the post-endocytic sorting of G-protein-coupled receptors between divergent and functionally distinct membrane pathways.
Tanowitz
Michael
M
Department of Psychiatry, University of California, San Francisco, California 94158-2140, USA
Hislop
James N
JN
von Zastrow
Mark
M
D000262:Adenylyl Cyclases / Q000235:genetics / Q000378:metabolism; D017398:Alternative Splicing / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation / Q000502:physiology*; D004705:Endocytosis / Q000502:physiology*; D006801:Humans; D020033:Protein Isoforms / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000235:genetics / Q000378:metabolism*
D020033:Protein Isoforms; D017450:Receptors, Opioid, mu; D000262:Adenylyl Cyclases